Ukraine has had hundreds of millions pumped into it (not to mention arms, which the Russians know are aimed at them) from a western direction to foment an anti-Russian attitude. An attempt to make it a western bulwark against Russia. Enough Ukrainians imagine they're soon going to be on the EU gravy train. Money works.
Many Russians, including more or less all those that currently matter, take the exact opposite view of Ukraine. For them, it's a bulwark against the west.
It doesn't take a genius to work out that, given the longstanding connections between the two places, that there will be Russians who, as I said, hardly differentiate between the two (except, maybe regarding the west of Ukraine), which results in two attitudes which might sometimes overlap-that Ukraine is 'ours' and that 'we shouldn't be fighting because they are our brothers and sisters.' Obviously this can translate into both 'take it back' and 'stop the fighting now.'